Television signal encoder utilizing a correlation between frames

Abstract

A television signal encoder uses correlation between frames for data compression or reduction in redundancy of information to be transmitted. The coding error occurring in the interframe coding process is effectively corrected by low-bit intraframe coding with limited increase in the volume of coding information. This permits raising the significance determination threshold value without impairment of picture quality.

What is claimed is: 
     
       1. A system for coding a television signal by the use of a frame correlation technique, said television signal consisting of a series of frames each defined by horizontal and vertical synchronizing signals and each representing a number of two-dimensionally arranged picture elements of an optical image to be transmitted, said coding system comprising: means for sequentially comparing every two successive frames to produce an interframe-coded signal;   means responsive to said interframe-coded signal and said television signal for obtaining an interframe-coding error signal caused in said comparing means;   means for coding said interframe-coding error signal to produce an intraframe-coded signal; and   means for multiplexing said intraframe-coded signal with said interframe-coded signal.   
     
     
       2. A system for coding a television signal as recited in claim 1, wherein said means for sequentially comparing comprises: subtractor means receiving said television signal as one input and a signal corresponding to a preceding frame of the television signal as another input for producing a difference signal;   coder means connected to receive said difference signal and a threshold signal for generating an output when said difference signal exceeds said threshold signal; and   memory means connected to the output of said coder means for storing data for one frame of the television signal and providing an output to said other input of said subtractor means.   
     
     
       3. A system for coding a television signal as recited in claim 2, further comprising a buffer memory means connected to receive the output of said means for multiplexing for temporarily storing information data occurring in an irregular fashion and providing said threshold signal to said coder means as a function of said buffer memory means occupancy. 
     
     
       4. A system for coding a television signal as recited in claim 3, wherein said means for coding said interframe-coding error signal comprises binary quantization means employing a quantization level lower in value than said threshold signal, said quantization level being determined by a signal from said buffer memory means. 
     
     
       5. A system for coding a television signal as recited in claim 4, wherein said means for coding said interframe-coding error signal further comprises averaging means connected between said means for obtaining an interfame-coding error signal and said binary quantization means. 
     
     
       6. A system for coding a television signal as recited in claim 4, wherein means for coding said interframe-coding error signal further comprises: subtractor means connected between said means for obtaining an interframe-coding error signal and said binary quantization means; and   feedback means connected between the output of said binary quantization means and a second input to said subtractor means to form a differential pulse code modulator.